It has been recognized for some time that vigorous brushing of the teeth with excessive force can cause damage to tooth material and gum tissue. Consequently, there have been attempts in the prior art to produce toothbrushes that yield in response to excessive manual force on the handle.
Toothbrushes having a flexible neck located between the brush head containing the bristles and the handle have been disclosed in the prior art. For example, U.S. Pat. No. 759,490 issued to Yates on May 10, 1904 discloses a toothbrush having an interposed piece of flexible resilient material between a rigid brush head and handle. The object of the flexible resilient neck is to permit the bristle head to yield relative to the handle when excessive force is applied, thus reducing the danger of injury to the teeth and gums. Yates further discloses reinforcing the flexible resilient material of the neck with a second flexible resilient material, such as flat or round wire comprised of spring steel, encased within the first material.
U.S. Pat. No. 1,471,626 issued to Pachmayr on Oct. 23, 1923 discloses a toothbrush having two cantilever flattened springs supporting a bristle carrying portion. However, the purpose of the flattened springs is not to limit the forces transmitted to the teeth and gums, but to engage a boss which secures the bristle carrying portion in either a parallel or angular position relative to the brush handle.
U.S. Pat. No. 4,520,526 issued to Peters on Jun. 4, 1985 discloses a toothbrush having a flexible joint between the head portion and handle portion. This flexible joint permits the head portion to flex in a vertical plane relative to the handle portion. One means disclosed to produce such a flexible joint is by thinning the toothbrush body by removing material from the top and/or bottom of the toothbrush body. The thinning at the flexible joint weakens the flexible portion, permitting the head portion to flex relative to the handle portion during brushing. Alternatively, Peters discloses a hollow which extends horizontally through the body member of the toothbrush forming a flexible joint comprising a thin top resiliently flexible horizontal member and a thin bottom resiliently flexible horizontal member. The purpose is again to weaken the body member to form a flexible portion which permits the head portion to flex relative to the handle portion during brushing. The object of such prior art toothbrushes is to provide a brush head which deflects relative to the brush handle in direct response to applied pressure to avoid damaging tooth material and gum tissue. While actual executions vary, the technique of such prior art toothbrushes is to lessen the rigidity of the neck portion by removing material or by substituting a less rigid material in the neck portion. The principal of operation of such prior art flexible neck toothbrushes is the same, i.e., increasing the force on the handle results in a corresponding deflection of the brush head relative to the brush handle. For effective cleaning of the teeth, some pressure needs to be applied to the brush head by the user. With prior art flexible neck toothbrushes of the type described in the preceding paragraphs, deflection of the brush head corresponds directly to the applied force on the handle, i.e., the flexible joint connecting the handle and the brush head behaves as a simple spring constant. With no clear indication of excessive pressure, the user applies his or her customary manual force on the brush handle and compensates for the resulting deflection by adjusting to the resulting angle of the brush head relative to the handle.
Although the desired object of prior art flexible neck toothbrushes is to avoid damaging teeth or gums, the disclosed means for accomplishing this is to simply reduce the stiffness of the neck portion of the toothbrush and thereby force the user to compensate by bending the brush handle to a greater degree. In this respect, none of the aforementioned flexible neck toothbrushes of the prior art provide means to indicate excessive pressure other than some ambiguous amount of bending. Further, excessive bending of the brush head relative to the brush handle makes the toothbrush annoying to use, and the accompanying loss of brush control can itself result in tissue damage.
One attempt to overcome problems of the aforementioned type is disclosed in U.S. Pat. No. 4,476,604 issued to White et al. on Oct. 16, 1984. White discloses a pressure sensing device for holding a toothbrush for the purpose of indicating that a predetermined force is being applied against the teeth. Although the device provides a distinct signal upon attaining a predetermined force and further achieves this result with minimal deflection of the brush head relative to the handle, the solution disclosed by White is complex and requires an electric battery, a lightbulb and an electric circuit.